I bought flats from Old Navy that were a little too small. While I hemmed and hawed on whether to exchange them for a bigger size is all my free time the return period ended. Then I happened upon the above trick.
As I dried my hair this morning I put on a pair of chunky socks, put the shoes on over them then blow dried my shoes on the warmest setting for 5 minutes. I left the shoes and socks on until they cooled. Once cooled I removed the socks and low and behold they fit perfectly!